Illuminate\Database\Eloquent\Model::asDateTime PHP Method

    protected function asDateTime($value)
    {
        // If this value is already a Carbon instance, we shall just return it as is.
        // This prevents us having to re-instantiate a Carbon instance when we know
        // it already is one, which wouldn't be fulfilled by the DateTime check.
        if ($value instanceof Carbon) {
            return $value;
        }
        // If the value is already a DateTime instance, we will just skip the rest of
        // these checks since they will be a waste of time, and hinder performance
        // when checking the field. We will just return the DateTime right away.
        if ($value instanceof DateTimeInterface) {
            return new Carbon($value->format('Y-m-d H:i:s.u'), $value->getTimeZone());
        }
        // If this value is an integer, we will assume it is a UNIX timestamp's value
        // and format a Carbon object from this timestamp. This allows flexibility
        // when defining your date fields as they might be UNIX timestamps here.
        if (is_numeric($value)) {
            return Carbon::createFromTimestamp($value);
        }
        // If the value is in simply year, month, day format, we will instantiate the
        // Carbon instances from that format. Again, this provides for simple date
        // fields on the database, while still supporting Carbonized conversion.
        if (preg_match('/^(\\d{4})-(\\d{1,2})-(\\d{1,2})$/', $value)) {
            return Carbon::createFromFormat('Y-m-d', $value)->startOfDay();
        }
        // Finally, we will just assume this date is in the format used by default on
        // the database connection and use that format to create the Carbon object
        // that is returned back out to the developers after we convert it here.
        return Carbon::createFromFormat($this->getDateFormat(), $value);
    }

 /**
  * Retain DateTime format for storage.
  *
  * @param \DateTime $value
  *
  * @return string
  */
 public function fromDateTime($value)
 {
     if ($value instanceof DateTime) {
         return $value;
     }
     return parent::asDateTime($value);
 }